Organopolysiloxane compositions having such properties are described, for example, in U.S. Pat. No. 4,191,817 to Schiller et al. These compositions crosslink when they are exposed to atmospheric moisture. Generally, the crosslinking occurs initially at the surface of such compositions with the formation of an outer skin and then continues inward until the composition has completely vulcanized. These compositions are used for coatings, as adhesives and as sealants.
In contrast to the compositions described, for example, in U.S. Pat. No. 4,191,817, the compositions of this invention crosslink and form elastomers when exposed to moisture, however, formation of the outer skin has been substantially delayed while at the same time the cure rate is substantially the same as conventional room temperature curable compositions.
It has been found that by the addition of mercapto-functional silanes or siloxanes that the formation of skin on the surface of the room temperature curable compositions may be substantially delayed without substantially effecting the overall cure rate of the composition.
Therefore, it is an object of the present invention to provide a composition which cures in the presence of atmospheric moisture. Another object of the present invention is to provide a composition which is stable under anhydrous conditions, but cures to an elastomeric solid when exposed to atmospheric moisture. A further object of the present invention is to provide a composition in which the outer skin formation is retarded, but cures at a rate which is comparable to conventional organopolysiloxane compositions. A still further object of the present invention is to provide a composition which may be used in screen printing processes.